1. Field of the Invention
The present invention relates to a method for continuous rolling by continuously welding the rolled materials at an intermediate stage of a rolling line after applying several passes of rolling of billets, and relates to an apparatus therefor.
2. Description of the Related Art
A known continuous rolling method to produce wire, rod, or to shape steel with energy-saving and high efficiency comprises the steps of discharging billets from a heating furnace one at a time, welding the rear end of a preceding billet with the front end of a succeeding billet by a single unit travelling flash-butt welder, removing the burr from the welded portions using a scarfer or the like, heating the thus formed continuous billet to a temperature necessary for rolling in an induction heating furnace, then continuously rolling the continuous billet in a rolling mill group: (disclosed in, for example, unexamined Japanese patent publication No.52-43754 (1977)). Alternatively, there is a continuous rolling method in which billets discharged from a heating furnace are joined together by welding to form a continuous billet, and the continuous billet is heated again in the heating furnace, wherein also a single unit travelling flash-butt welder is used: (disclosed in, for example, examined Japanese patent publication No.52-11722 (1982)).
Shortening the cycle time for treating a single billet is an important issue in the continuous rolling of billets. In this respect, the weight of an ordinary billet is in a range of from 0.5 to 2 ton, and the necessary cycle time to treat a single billet is less than 1 min. to assure a production capacity of 70 to 80 ton/hr or more. Since conventional continuous rolling processes use only one on-line travelling flash-butt welder, as described above, the welding time inherent to the travelling flash-butt welder is difficult to shorten. Consequently, it is impossible to realize a cycle time of less than 1 min. in the prior art.
A possible method to shorten the time cycle is to incorporate two travelling welder units to realize a shorter cycle time operation. However, a system of two travelling welders increases investment cost and requires large capacity of power source. Another possible method is to reduce the cross sectional area of the billet through rolling in a specific number of rolling mill groups, to provide the intermediate rolled materials in a free state, to adjust the position of the intermediate rolled materials, and to perform the weld-joining to reduce the welding time. These methods, however, have a disadvantage that, when the intermediate rolled materials become long, the methods cannot be adopted-owing to the limitation of interstand distance:
An object of the present invention is to provide a method of continuous rolling which shortens the cycle time of billet treatment without requesting a large-scale modification of existing facilities, and to provide an apparatus therefor.
The first method for continuous rolling comprises the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after being rolled in the first rolling mill group by a set of pinch rolls, detecting the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; removing burr from a welded section on the continuous material; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step.
The first apparatus of continuous rolling comprises: a first rolling mill group for successively rolling a plurality of materials; a travelling welder for joining a rear end of a preceding material with a front end of a succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the materials; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a second rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; wherein the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.
The second method for continuous rolling comprises the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after being rolled in the first rolling mill group by a set of pinch rolls, controlling the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; grinding a welded section on the continuous material to remove burr therefrom; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step.
The second apparatus for continuous rolling comprises: a first rolling mill group for successively rolling a plurality of materials; a set of pinch rolls for pinching a succeeding material after being rolled and for detecting the transfer speed of the pinched material; a front end detector located at inlet of the pinch rolls for detecting a front end of the succeeding material; a measuring roll for detecting the transfer speed of a preceding material which is transferred before the succeeding material; a rear end detector located at inlet of the measuring roll for detecting a rear end of the preceding material; a travelling welder located at down-stream side of the measuring roll for joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the continuous material; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a secondary rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; and a drive control unit to which signals from the pinch rolls, the front end detector, the measuring roll, and the rear end detector are entered, and in which the rotational speed of the pinch rolls or both the rotational speed of the pinch roll and the rolling speed of the first rolling mill group are determined so as to enable the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder, and these determined variables are controlled; wherein the pinch rolls, the measuring roll, the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.